docs: def is_opendap(url):
      '''
      Returns True if the URL is a valid OPeNDAP URL
  
      :param str url: URL for a remote OPeNDAP endpoint
      '''
      # If the server replies to a Data Attribute Structure request
      if url.endswith('#fillmismatch'):
          das_url = url.replace('#fillmismatch', '.das')
      else:
          das_url = url + '.das'
      response = requests.get(das_url, allow_redirects=True)
      if 'xdods-server' in response.headers:
          return True
      # Check if it is an access restricted ESGF thredds service
      if response.status_code == 401 and \
          'text/html' in response.headers['content-type'] and \
              'The following URL requires authentication:' in response.text:
          return True
      return False